Automatic wrapping or packaging machines are designed to wrap products in flexible sheets of plastic film, typically heat sealable thermoplastic shrink film, fully automatically at speeds that can approach 200 linear feet per minute, depending upon the package and the application. Briefly, products to be packaged are continuously fed into the wrapping machine on a conveyor. A single sheet of flat film is delivered to a forming plow from an overhead powered film unwind or an inverting head from a rear powered film unwind. The size and shape of the forming plow or the inverting head depends upon the size and profile of the product to be packaged. As the film is drawn over the forming plow or the inverting head, it is inverted and forms a tube of film inside the forming plow or the inverting head into which the product is conveyed. The product enters this tube of web material and the product itself serves to maintain the shape of the tube as the product and film then continues through the machine in unison. The two edges of the single web of film are overlapped on the bottom, side, or top of the product and are sealed together, such as with a static sealing system or a thermal sealing system. The product passes through end seal jaws that seal in between the packages and concurrently sever individual packages from the tube of film. The wrapped package then typically proceeds to a shrink tunnel located at the discharge end of the wrapping machine, which shrinks the thermal film tightly around the product. Occasionally, the wrappers are used to perform containment bagging functions only without the use of a shrink tunnel.
Wrapping or packaging machines that utilize two webs of material, one fed from above the product and one fed from below, that automatically wrap around the product and are sealed also are known.
One example of conventional automatic wrapping machines that uses an inverting head instead of a plow to invert the film and form the tube into which the product is conveyed is shown in U.S. Pat. No. 4,219,988. An inverter head is positioned at a 45° angle with respect to the direction of package flow, and the sheet of film fed from an unwind wraps around the head and is inverted (the outside surface of the film web becomes the inside as the web forms around the head). As the package emerges from the vicinity of the inverting head, the film is enveloped around it. The wrapped package proceeds to a thermal side seal unit, and eventually to the end seal unit.
Machines such as these function well for low profile products and are used pervasively for such applications. However, as the height or profile of the products to be packaged increases, the geometric shape and scale of size of the inverting head or the forming plow become unmanageable in size for practical use. The forming plow is affected by the width of the web passing over it. The inverting head is affected by the length of cantilever extension. As a result, significant web tracking problems arise from material handling issues of that scale. The result is substantial difficulty in the execution of the wrapping process, unattractive finished product, and/or complete inability to wrap product.
It is therefore an object of the present invention to provide an apparatus and method for effectively wrapping high profile products.
It is another object of the present invention to provide a guide system for guiding the webs to form and maintain a predetermined geometric shape, independently of the location of the product, the shape being configured to envelope a product to be packaged.
It is a further object of the present invention to provide an apparatus and method for reliable and quality automatic wrapping of products utilizing two webs of flexible, sealable material while avoiding web-tracking problems.
Other objects and features of the present invention will become apparent from the following description and drawings.